Method of increasing the work function of metal parts for example for electric discharge tubes



United States Patent METHOD OF INCREASING THE WORK FUNCTION OF METALPARTS FOR EXAMPLE FOR ELEC- TRIC DISCHARGE TUBES No Drawing. ApplicationNovember 22, 1954 Serial No. 470,554

Claims priority, application Netherlands December 1, 1953 1 (llaim. (Cl.148-4) Discharge tubes frequently contain metal parts which are at lowpotential and other metal parts which are at higher potential and whichare arranged at close proximity to one another, for example electrodesof nickel or stainless steel in a monopotential lens for televisionpicture tubes. It, now, the field strength resulting from the existingdifference in potential becomes greater than the work-function of themetal parts, unwanted scattered radiation occurs. For this reason onehas looked for metallic parts having as high a work-function aspossible. The Work function of a material is an indication of the energyrequired to extract electrons therefrom. Efforts have been made to solvethis problem not only by varying the chemical composition of the metalsused therefor, but also by particular shaping thereof. In shapingprojecting edges and collars exhibiting a so-called point action werepreferably avoided. Furthermore, it has been suggested to polish themetal parts by electrolytic means. Although it has been found thatpolishing of the surfaces of the parts in itself raises the workfunction, this method suffers from the disadvantage that an oxide layerusually occurs at the surface and this results in a decreased workfunction.

The present invention relates to a method of increasing the workfunction of metal parts, for example for electric discharge tubes, whichdo not suifer from the above-mentioned disadvantages. The inventionexhibits the characteristic that the surfaces of the metal parts aresubjected to the action of ultrasonic radiation.

An explanation for the occurrence of the said effect cannot be givenwith certainty. It may be that the ultrasonic radiation has amicro-polishing action.

Another explanation may be that the oxide layer which may occur on theouter surface is removed by the ultrasonic radiation.

It has been found advantageous to carry out the method according to theinvention in such manner that the metal parts to be treated are immersedin a liquid and that the ultrasonic radiation is produced in this bath.It is preferable to utilise a liquid which cannot exert an oxidizinginfluence upon the surfaces of the metal parts.

Furthermore, it has been found that a still higher work-function isobtained if the metal parts, before proseeding to the ultrasonictreatment, are polished and preferably polished electrolytically.

Several applications of ultrasonic irradiation are already known. Thus,for example, it has been suggested to remove fat or dirt from surfacesunder the action of such radiation. Furthermore, ultrasonic radiationhas been used for coating aluminium with tin. In this case it has beensuggested to keep an aluminium object in a bath of molten tin and toproduce therein a field of ultrasonic radiation, the action of theultrasonic irradiation consisting in. removing the oxide layer from thealuminium.

Objects treated by the method according to the invention have been foundto be very suitable for use in electric discharge tubes in which theobjects have to resist high tensions, for example higher than 20kilovolts.

Example Electrodes for a monopotential lens for television picture tubeswere subjected to ultrasonic radiation in a bath of ethyl alcohol forseveral minutes. The frequency was 26,000 kc./s. and themagnetostriction core was fed with 50 watts. After this treatment anddrying of the surfaces, the work-function of the electrodes was found tobe approximately from 20% to 25% higher than that before the treatment.

What is claimed is:

A method of increasing the work function of the surface of a metalmember, which comprises first electrolytically polishing the surface ofsaid member adapted for use as an electrode of an electric dischargetube, and thereafter immersing said member in a non-oxidizing liquidbath and subjecting it to ultrasonic radiation while in said bath toincrease the work-function of said electrode.

References Cited in the file of this patent UNITED STATES PATENTS1,939,712 Mahoux Dec. 19, 1933 2,329,317 Atlee Sept. 14, 1943 FOREIGNPATENTS 548,960 Great Britain Oct. 30, 1942 OTHER REFERENCES GeneralElectric Review, March 1952, vol. 55, No. 2, pages and 61.

Bright Future for Ultrasound by J. A. Antonevich, Bettelle Tech. Review,vol. 5, No. 4, April 1956, pages 9-13.

1. A METHOD OF INCREASING THE WORK FUNCTION OF THE SUR FACE OF A METALMEMBER, WHICH COMPRISES FIRST ELECTROLYTICALLY POLISHING THE SURFACE OFSAID MEMBER ADAPTED FOR USE AS AN ELECTRODE OF AN ELECTRIC DISCHARGETUBE, AND THEREAFTER IMMERSING SAID MEMBER IN A NON-OXIDIZING LIQUIDBATH AND SUBJECTING IT TO ULTRASONIC RADIATION WHILE IN SAID BATH TOINCREASE THE WORK-FUNCTION OF SAID ELECTRODE.